The present invention relates to a method for predicting temperature, a test wafer for use in temperature prediction, and a method for evaluating a lamp heating system using the test wafer. More particularly, this invention provides measures to predict more accurately the actual temperature or temperature distribution of a wafer to be loaded into the lamp heating system.
A method for predicting the actual temperature of a wafer to be loaded into a thermal system, in which the wafer should be subjected to intense heat in a semiconductor device fabrication process, was disclosed in PCT International Publication No. WO 98/57146.
In the Publication, an amorphous layer is formed in the uppermost part of a silicon wafer by implanting ions. Then, the silicon wafer including the amorphous layer is loaded into a thermal processing system and heated therein. In this manner, the actual temperature of the silicon wafer is predicted.
The present inventors carried out various experiments on the known method for predicting temperature. As a result of these experiments, it was found that the actual wafer temperature could not be predicted accurately enough by the known method when the method was applied to a lamp heating system as described later.
It is therefore a first object of the present invention to predict accurately the actual temperature or temperature distribution of a wafer to be loaded into a lamp heating system.
It is a second object to evaluate whether or not the lamp heating system including a lamp is affected by light emitted from the lamp and transmitted through the wafer.
In order to achieve the first object, according to the present invention, a method is used for predicting, using a test wafer, a temperature of a wafer to be loaded into a lamp heating system including a lamp. The method includes the steps of: a) preparing the test wafer, which includes a first semiconductor layer formed in a crystalline state, a second semiconductor layer formed in an amorphous state on the first semiconductor layer, and a light absorption film formed over the second semiconductor layer; b) loading the test wafer into the lamp heating system and then irradiating the test wafer with a light emitted from the lamp, thereby heating the second semiconductor layer through the light absorption film; c) calculating a recovery rate at which a part of the second semiconductor layer that has been heated recovers from the amorphous state to the crystalline state at the interface with the first semiconductor layer; and d) measuring a temperature of the test wafer that has been irradiated with the light, according to a relationship between the recovery rate and a temperature corresponding to the recovery rate.
According to the inventive method, a test wafer for use in temperature prediction includes a light absorption film formed over an amorphous second semiconductor layer. The light absorption film absorbs light that has been emitted from a lamp and transmitted through a first and the second semiconductor layers not to contribute a thermal process performed on the semiconductor layers. Thus, a recovery rate for obtaining the actual wafer temperature can be calculated much more accurately by the thickness of the second semiconductor layer subjected to heat. As a result, the actual temperature of the wafer loaded into a lamp heating system can be predicted accurately.
In one embodiment, at least a part of the light may have a wavelength at which the first semiconductor layer transmits the light. Then, the effects of the present invention can be obtained as intended.
In this particular embodiment, the light preferably has a wavelength at which the first semiconductor layer has a transmittance to the light and the transmittance increases at a temperature range. Then, the effects of the present invention can be obtained as intended.
In another embodiment, the light may have a wavelength from about 1.0 xcexcm to about 3.0 xcexcm, both inclusive.
In still another embodiment, the first semiconductor layer and the second semiconductor layer may be made of silicon and the light absorption film may be made of a conductive film containing a metal.
In this particular embodiment, the light absorption film is preferably made of a metal that is usable for forming a silicide and the lamp heating system is preferably used for a silicidation process. Then, the light absorption film acts as a metal film to be used for the silicidation process. Thus, wafer temperature prediction can be performed under the same conditions as in the silicidation process.
In this particular embodiment, the temperature range is preferably from about 450xc2x0 C. to about 600xc2x0 C., both inclusive.
In this particular embodiment, the test wafer preferably includes a barrier film that prevents the second semiconductor layer and the light absorption film from reacting together. This barrier film is preferably formed between the second semiconductor layer and the light absorption film.
In yet another embodiment, the test wafer may have a diameter of about 30.5 cm (12 inches) or more.
An inventive test wafer is used for predicting a temperature of a wafer to be loaded into a lamp heating system. The test wafer includes: a first semiconductor layer formed in a crystalline state; a second semiconductor layer formed in an amorphous state on the first semiconductor layer; and a light absorption film formed over the second semiconductor layer.
In one embodiment, the test wafer may further include a barrier film that prevents the second semiconductor layer and the light absorption film from reacting together. This barrier film may be formed between the second semiconductor layer and the light absorption film.
In another embodiment, the test wafer may have a diameter of about 30.5 cm (12 inches) or more.
In order to achieve the second object, an inventive method is used for evaluating a lamp heating system including a lamp. Specifically, this method, which utilizes a transmittance to a light emitted from the lamp, is used for evaluating whether or not respective temperatures of a first test wafer and a second test wafer loaded in the lamp heating system are affected by the light. The method includes the step of a) preparing: the first test wafer including a first semiconductor layer formed in a crystalline state and a second semiconductor layer formed in an amorphous state on the first semiconductor layer; and the second test wafer including a third semiconductor layer formed in a crystalline state, a fourth semiconductor layer formed in an amorphous state on the third semiconductor layer, and a light absorption film formed over the fourth semiconductor layer. The method also includes the step of b) loading the first test wafer and the second test wafer into the lamp heating system and then irradiating the first test wafer and the second test wafer with the light, thereby heating the second semiconductor layer and heating the fourth semiconductor layer through the light absorption film. The method further includes the step of c) obtaining a first rate of variation in thickness of the second semiconductor layer with respect to a period of time in which the second semiconductor layer is subjected to heat, and obtaining a second rate of variation in thickness of the fourth semiconductor layer with respect to a period of time in which the fourth semiconductor layer is subjected to heat. The method further includes the step of d) comparing the first rate with the second rate, thereby judging that the temperature of the first test wafer is not easily affected by the light transmitted through the first test wafer if the first rate is equal to the second rate, while judging that the temperature of the first test wafer is easily affected by the light transmitted through the first test wafer if the first rate is smaller than the second rate.
According to an inventive method for evaluating a lamp heating system, variation in thickness of a second semiconductor layer (amorphous layer) in a first test wafer including no light absorption film and that of a fourth semiconductor layer (amorphous layer) in a second test wafer including a light absorption film are compared with each other. Then, whether or not the lamp heating system is easily affected by light emitted from the lamp and transmitted through the semiconductor layers.
In this case, the system that is easily affected by the light is a system in which the first test wafer transmits a relatively large amount of the light and thus has its real temperature differ greatly from a temperature indicated by a thermometer made up of, for example, a thermocouple provided in the system.